Automatic telephone system



1942- G. E. STOVNEBRIDGE, JR- 2,299,650

AUTOMAT IG TELEPHONE SYSTEM Filed June 25, 1941 GEN NVENTOR.

I GEORGE E STONEBRIDGE JR.

ATTORNEY Patented Oct. 20, 1942 AUTOMATIC TELEPHONE SYSTEM George E.Stonebridge, In, New York, N. Y., as-

signor to Associated Electric Laboratories, Inc., Chicago, 111., acorporation of Delaware,

Application June 23, 1941, Serial No. 399,266

6 1 Claims.

- used in such systems.

More in particular the invention may be considered as a directimprovement in the ringing arrangements using grounded interruptedgenerator, such as shown in the Lomax Patent 1,569,430, issued January12, 1926. In this Lomax patent the ringing circuit extends from groundedgenerator, the common interrupter springs, to normally closed backcontacts on the ring-cut-off relay of the connector, and through makecontacts on the switching relay to the lower, or positive, line wiper.In case this wiper encounters a grounded positive line conductor, or incase any portion of the above described circuit becomes grounded,trouble occurs. That "is, this fault ground may substantiallyshort-circuit the generator thereby causing damage to it, provided aprotecting resistance, such as a series lamp, is not provided in theringing circuit. In addition, when the generator is ringing on agrounded ringing circuit on one connector switch all other connectorsusing this same generator are deprived of ringing current due to thefirst connector shunting the ringing supply to ground. This conditionexists until the subscriber using this first connector hangs up.

The main object of the invention is to overcome the above-mentioneddefects by providing circuits such that the ringing circuit is out Ohwhen a grounded line is encountered. In the instant case, a marginalrelay is provided in the ringing circuit which will not operate onnormal maximum ringing current transmitted over the line conductorsthrough the -condenser and ringer at the substation and the upperwinding of the connector cut-off relay, but which will operate when theconnector rings to ground on a defective line. This marginal relayoperates to cause the energization of the connector ring-cut-ofi relayto disconnect the generator whenever the lower, or positive, line wiperencounters a grounded positive line conductor.

The means by which the foregoing object is accomplished will be fullyset forth hereinafter,

reference being had to the accompanying drawing which shows sufiicientof the apparatus to enable the invention to be explained and understood.

Referring now to the drawing, it should be stated that only the ringingcircuit of the presrelay 33, release relay 34, ring-cut-off relay 31,switching relay 4!), and the common ringing generator Gen. andinterrupter Int. are identical to the correspondingly numbered relaysand ringing machine RM shown in the connector H in the Lomax Patent1,569,430. The only addition to this circuit is the marginal relay 4|and its make contacts 42 for operating the ring-cut-ofi relay. Thesubstation A corresponds to the substation A shown in theabove-mentioned Lomax patent. PI and F2 represent faults, which for thepurpose of explaining the invention, ground either line conductor M2 or2 of substation A.

Having given a brief'description of the apparatus, the operation of thesame will now be described in detail. For this purpose it will beassumed that the connector switch including the ringing circuit of thedrawing is seized and operated in the same manner as described in Patent1,569,430. Upon seizure of this connector the line relay 33 energizesand operates release relay 34 over an obvious circuit. In response todialling the two digits of the called line, the wipers BI and 83 areoperated to the bank contacts 84 and 8B and the switching relay 40 isenergized and locked energized in case the called line is idle asdescribed in the Lomax patent. In response to the operation ofswitching-relay 40 the new ringing circuit is closed. This circuitincludes grounded generator and interrupter make contacts 75 of thecommon ringing machine RM, through the added marginal relay 4|, backcontacts 51 of the ring-cut-off relay 31, make contacts 61 of switchingrelay 40, lower, or positive, line wiper 83, bank contact 88, positiveline conductor 212, through the condenser C, ringer R andnormally-closed switch-hook contacts of substation A, negative lineconductor 2| bank contact 84, negative line wiper 8 I, make contacts 63,back contacts 55 and through the upper winding of ring-cut-ofi relay 31to the common grounded battery. The ring-cut-ofi relay, as is wellknown, does not operate in this circuit due to the copper slug on itsarmature end and its copper sleeve. The new marginal relay is of suchvalue that it also will not operate over the above-traced circuitincluding the ringer R and the upper winding of ring-cut-ofi relay 31.The copper slug on the heel end of relay 4| is provided to lower theimpedance of this relay so as not to effect the ringing current. Inresponse to the operation of the ringer R subscriber A responds byremoving his receiver thereby disconnecting the ringer R and conentinvention is fully disclosed andthat line 55 denserC and substituting adirect current path through substation A for energizing ring-cut-offrelay 31. The marginal relay 4| is also included in this energizingcircuit for the ring-cut-oif relay and it is immaterial whether thismarginal relay 4| operates or not since its only function is to operatethe ring-cut-ofi relay which operated over the called subscribers loop.

The operation of the ring-cut-ofi relay 3'! completes the talkingcircuit between the calling and called subscribers lines as described inthe Lomax patent.

In both the Lomax Patent 1,569,430 and Wicks Patent 1,667,915 thecircuits of the ring-cut-off relays are such that these relaysareenergized in case the upper, or negative, line Wiper encounters ground.The circuit for energizing the ring-cut-off relay 31 of the said Lomaxpatent is the same as the drawings shown inthe instant application andmay be traced as follows: from the fault ground, such as F2, negativeline conductor 2| l, bank contact 84, negative line wiper 8|, contact63, back contacts 55, and through the upper winding of ring-cut-offrelay 3? to battery. The circuit for energizing the ring-cut-oii relayin Wicks Patent 1,667,915 may be traced from the fault ground on theupper or negative, line conductor, connector bank 4%, negative linewiper 45B, armature spring 435 and its front contact of switching relaytill, armature spring 425 and its back contact of ring-cut-ofi relay 6%,upper winding of ring-cut-off relay G64, and through the interruptersprings of the ringing machine to battery connected generator. From theforegoing it will be seen that it is customary to operate thering-cut-ofl relay and disconnect ringing current from the called linewhenever a faulty ground is encountered by the upper, or negative, linewiper of the connector switch.

In accordance with the present invention circuit arrangements are shownfor causing the operation of the ring-cut-off relay to disconnectringing current when the lower, or positive, line wiper of the connectorencounters a faulty ground on the positive line conductor of the calledline. Therefore, with the circuits as shown in the instant application,the ring-cut-off relay of the connector'is automatically operated to cutoff the ringing current in response to either the negative or positiveline wiper encountering a faulty grounded line conductor.

It will now be assumed that the connector wipers 8i and 83 have beenconnected to bank contacts 84 and 88, that the switching relay 40 hascompleted the ringing circuit, and that the positive line conductor H2is grounded at El by a faulty ground. Under this condition the followingcircuit exists: from grounded generator, interrupter make contacts 15 ofthe common ringing machine RM, through the marginal relay 4|, restingcontact and armature spring 57, contacts 6'1, positive line wiper 83,bank contact 88, and positive line conductor 252 to the fault ground atFl. Marginal relay 4| is energized in this circuit and at contacts 52completes a circuit through the lower winding of cut-01f relay 31 tocause the latter relay to energize and disconnect the generator from thegrounded line conductor at armature spring Relay 3'! at contacts 56completes a locking circuit for itself from the release trunk ground atarmature 5! of release relay 34 so that relay 3? is maintained operatedafter relay H deenergizes which it does when its energizing circuit isopened at contact 51. During the period that the grounded generator isringing to ground on the positive line,

a partial short circuit exists through the generator which would beharmful thereto if the same persisted. However, since relay 4| causesthe operation of relay 3'! this partial short circuit is of such shortduration that no harm is done to the generator. Also, during this shortperiod, the ringing current is shunted to ground thereby depriving allother connectors of ringing current which at the time are in'ringingposition, but this period is now of such short duration, due to theoperation of the cut-off relay, as to be negligible.

Having described my invention, what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What I claim is:

1. In a telephone system, a called line having a pair of lineconductors, a connector switch having a pair of line wipers, means forconnect ing said line wipers with said line conductors, means fortransmitting ringing current over said line conductors to signal thecalled subscriber, a ring-cut-off relay in said connector operated inresponse to the called subscriber answering for disconnecting saidringing current from the called line, said ring-cut-off relay alsooperative in case a particular one of said line wipers encounters agrounded line conductor and also operative in case the other line wiperencounters a grounded line conductor for disconnecting ringing currentfrom the called line whereby irrespective of which line conductor isgrounded said ring-cut-oif relay is operated to disconnect ringingcurrent.

2. In a telephone system, a called line having a pair of lineconductors, a connector switch having a pair of line wipers, means forconnecting said line Wipers with said line conductors, means fortransmitting ringing current over said line conductors to signal thecalled subscriber, a ring-cut-oif relay in said connector operative todisconnect said ringing current from the called line, and means foroperating said cut-off relay under any one of the following conditions,first, in response to the called subscriber answering, second in caseone of said line wipers encounters a grounded line conductor, and thirdin case the other of said line wipers encounters a grounded lineconductor.

3. In a telephone system, a called line having a pair of lineconductors, means for connecting with said line conductors and fortransmitting ringing current over said line conductors to signal thecalled line, a ring-cut-oif relay operative to disconnect said ringingcurrent from the called line, and means for operating said ringcut-oifrelay under any one of the following conditions: first, in response tothe called subscriber answering, second, in case a particular one ofsaid line conductors is grounded, and third, in case the other of saidline conductors is grounded.

4. In a telephone system, a called line including a pair of lineconductors and a bridged ringer, a battery having one pole thereofgrounded, a generator connected to the grounded pole of said battery,means for connecting with said line conductors, a series ringing circuitincluding the grounded pole of said battery, said generator, the windingof a marginal relay, a particular one of said line conductors, saidbridged ringer, the other of said line conductors, the Winding of aring-cut-off relay, and the opposite pole of battery, means forcompleting said circuit to signal the called subscriber, said marginalrelay being unresponsive to the normal ringing current in said circuittransmitted from said generator through said ringer and the winding ofsaid ring-cut-ofi relay and operative only in case said particular oneof said line conductors is grounded, said ring-cutofi relay also beingunresponsive to the normal ringing current in said circuit transmittedfrom said generator through said ringer and operative in response to thecalled subscriber disconnecting said bridged ringer and substituting adirect current bridge across said conductors and also operative duringsaid ringing period in case said other line conductor is grounded, meansoperated by said ring-cut-off relay for disconnecting said generatorfrom said line conductors, and means responsive to the operation of saidmarginal relay for operating said ring-cut-ofi relay to disconnect saidgenerator from the called line.

5. In a telephone signalling system, a called line having a pair of lineconductors; a ringing circuit including a grounded generator, a marginalrelay, said line conductors, and a ring-cutoif relay; means forcompletin said circuit to signal the called subscriber over said lineconductors, said marginal relay operated in said circuit by saidgrounded generator only in case a particular one of said line conductorsis grounded, and means responsive to the operation of said marginalrelay for operating said ring-cut-ofi relay to disconnect said generatorfrom the called line conductors.

' 6. In a telephone signalling system, a called line having a negativeline conductor and a positive line conductor; a series ringing circuitincluding a grounded generator, a marginal relay, said positive lineconductor, the called subscriberfs ringer, said negative line conductor,a

'ring-cut-ofi relay and a battery having one pole grounded; means forcompleting said circuit to operatesaid called subscribers ringer, saidmarginal relay operative in said circuit by said grounded generator onlyin case said positive line conductor'is grounded, and means controlledby the operation of said marginal relay for operating said ring-cut-ofirelay to open said circuit thereby disconnecting said generator fromsaid grounded positive line conductor.

GEORGE E. STONEBRIDGE, JR.

